1. Field of the Invention
The present invention relates to a semiconductor device including a semiconductor element of a high breakdown voltage. More particularly, the present invention relates to a semiconductor device having an active element of low speed performance and high breakdown voltage combined with an active element of high speed performance and low breakdown voltage to operate in high performance and high breakdown voltage.
2. Description of the Background Art
Recently, it has become possible to fabricate high frequency (RF) circuits using CMOS semiconductors according to the submicron technology of semiconductors. However, it has become difficult to satisfy both the requirement of favorable performance and reliability for voltage control oscillators (VCO), mixers (MIX), power amplifiers (PA) and the like of high voltage since the gate breakdown voltage between the gate and drain is reduced by microminiaturization.
In view of the foregoing, the approach of connecting CMOS semiconductor devices in a cascade manner shown in FIG. 3 has been employed. Specifically, to an NMOS transistor 1 having an input voltage Vin applied to its gate, a same NMOS transistor 2 is cascade-connected. An inductor 3 is connected between the drain of NMOS transistor 2 and the power supply line as a load. An output signal Vout is provided from the drain of NMOS transistor 2.
In the circuit shown in FIG. 3, the voltage amplitude of the drain of NMOS transistor 2 to which inductor 3 is connected swings about the power supply voltage. This voltage amplitude becomes greater in proportion to greater power. During this great voltage amplitude, a potential difference greater than the power supply voltage is generated between the gate-drain of the upper stage NMOS transistor 2. There is a limit in raising the gate breakdown voltage. The gate breakdown voltage will be insufficient, so that the reliability cannot be satisfied.